This application relates to the art of film forming compositions and to methods for applying films to substrates. The invention is particularly applicable to film forming compositions that contain solid state alkylsilsesquioxane polymers and to methods for applying such polymers to substrates, and will be described with particular reference thereto. However, it will be appreciated that the application has broader aspects and that at least certain features can be used with other polymers and methods.
Polymerizable amphiphilic molecules having the intrinsic ability to self-assemble into a thin film are well known in both solution phase and gas phase. By way of example, descriptions of such materials and their ability to form thin films are contained in: W. C. Bigelow et al, J. Colloid. Sci., 1,513-538 (1946); L. H. Lee, J. Colloid. & Interface Sci., 27, 751-760 (1968); E. E. Polymeropoulos et al, J. Chem. Phys., 69, 1836-1847 (1978); J. Sagiv, U.S. Pat. No. 4,539,061; J. Phys. Chem. 70, 2937 (1966); Trans. Faraday. Soc., 63, 2549 (1967); J. Phys. Chem., 73, 2372 (1969); Langmuir, 7, 923 (1991); Langmuir, 9, 3518 (1993) and Langmuir, 13, 1877 (1997). Disclosures of molecular beam deposition of coatings on substrates are found in the following U.S. Pat. Nos. 4,001,858; 4,181,544; 4,330,360; 4,681,773; 4,800,100; and 5,064,520. The disclosures of these publications and patents are hereby incorporated herein by reference. Compositions and methods for applying hydrophobic ultra thin films of self-assembling amphiphilic molecules to substrates are described in commonly assigned U.S. Pat. Nos. 5,078,791; 5,166,000; 5,173,365; 5,204,126; 5,219,654; 5,300,561; 5,766,698; and 5,897,918. The disclosures of these patents are hereby incorporated herein by reference.
Use of the compositions and methods disclosed in the above literature and patents typically results in the formation of a mono-layer thin film on a substrate surface. Inter-molecular interactions in both solution phase and gas phase under a low vacuum make it difficult to use these compositions and methods to form multi-layer films. In addition, the use of these compositions requires cleaning of the substrate surface and/or the vacuum chamber after formation of the film.
Compositions and methods disclosed in the above literature and patents are very sensitive to moisture, and require special packaging, handling and processing. These prior art processes also expose the entire substrate surface to the film forming substance and result in a film over the entire surface of the substrate. There is no choice of selecting a certain substrate surface or shape for film formation other than by masking.
In the compositions and methods disclosed in the above literature and patents, highly reactive self-assembling amphiphilic monomer substances are used to form the films. It would be desirable if these monomers could be partially polymerized to reduce their high reactivity to moisture while still being capable of acting as self-assembling amphiphilic molecules to form thin films.
Compositions with organic polymer molecules and self-assembling amphiphilic polymer substances for use in forming multi-layer thin films have been reported in the literature. By way of example, silsesquioxanes made from different monomer silanes and alkylsilanes are disclosed in Chem. Rev., 95 1431-1442 (1995) and Chem. Rev., 95, 1409-1430 (1995), and references cited therein and in J. Am. Chem. Soc., 119, 3135-3143 (1997). The disclosures of these publications are hereby incorporated herein by reference.
Methods for applying multi-layer thin films of organic polymers and self-assembling amphiphilic polymer substances inside ultra high vacuum chambers are known in the fields of optoelectronics, flat panel displays, thin film transistors and lasers as disclosed in J. Am. Chem. Soc., 120, 8563-8564 (1998) and Chem. Rev., 97, 1793-1896 (1997), and references cited therein. The disclosures of these publications are hereby incorporated herein by reference.
Use of the above methods and compositions requires the use of materials having extremely high purity. Therefore, a very complicated purification procedure is required that includes the use of a vacuum chamber at an ultra high vacuum of 1×10−7 to 1×10−11 torr.
It would be desirable to have a process and composition for use in applying hydrophobic thin films of self-assembling amphiphilic polymer substances to surfaces in a manner that is very fast, efficient and cost effective. It also would be desirable to have a process that is capable of coating only one surface at a time with a film of controlled thickness. It also would be desirable to have a process that could be used at a much lower vacuum than the ultra high vacuum mentioned in the previous references. It also would be desirable to have a process where cleaning of the excess coating material inside the vacuum chamber automatically takes place during the coating process. It would be desirable to have a coating composition of self-assembling amphiphilic polymer substances that is easy to handle and use. It also would be desirable to have a composition that is very stable at room temperature and humidity, and does not require special protection from temperature or moisture. It would be yet another desirable characteristic to have a composition and process that is user friendly and environmentally safe. It would be another desirable characteristic to have a composition and process in which a single component material of very high purity is not required. It further would be desirable to have a coating composition that is easy to dispose of after it has been used.